Surface finish comparator



Dec. 12, 1944. E. J. ALMQUIST SURFACE FINISH COMPARATOR Filed March 3, 1942 Ephraim d Alm uat Patented Dec. 12, 1944 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) Y 1 Claim.

The invention described herein may be manu-- factured and used by or for the Goverment for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a surface finish comparator.

An object of this invention is to provide a surface finish comparator having spaced circular finish specimens thereon, preferably of the same outside diameter, with each specimen being of a different type of finish.

Another object of this invention is to provide a compact handy and useful instrument for comparing some of the various types of surface 1inishes which are produced in the arts with standard types of those finishes on the instrument.

Another object of this invention is to provide' a compact, handy and useful instrument for comparing the appearance of an article with the appearance of standard specimens on the instrument. n

The instrument which is the subject of this invention is useful in the testing and inspection cf finished articles, but it is useful also to the designer and fabricator of the article which is to have a certain finish. Besides being an instrument by means of which a particular appearance of an article may be ascertained, the instrument serves also as a qualitative standard for the particular finish under observation, i. e., the particular finish or surface on a fabricated article may be compared with the finish or surface of standard specimens on the instrument in inspection operations.

Another object of this invention is to provide a finish comparator for smooth fiat fabricated' articles as well as for rounded fabricated articles.

Another objectl .of this invention is to provide a finish comparator which is inexpensive to produce and which has replaceable finish specimens thereon.

Another object of this invention is to provide a finish comparator which also serves in helping to compare distances and heights of minute surface irregularities on fabricated articles and thus provide information which cannot be obtained or is not readily deducible by the standard profilometer or brush methods.

Another object of this invention is to provide a comparator which is adapted to accommodate one of a plurality of finish specimens which is Cut from a relatively large uniformly finished piece of stock.

A thread comparator for threaded fabricated parts is disclosed in my copending application Serial- No. 433,144, filed March 3, 1942, which discloses a structure similar to that shown in the drawing in this application, which application has eventuated in Patent No. 2,331,882.

The problem of surface finishes on fabricated articles is important in Athe mass production of interchangeable parts, also, where certain surfaces are to be painted and where surfaces are to be bolted together. Also, the accuracy with which dimensions of fabricated articles may be made, since such measurements involve a contact with the fabricated article, appears to be a function of the surface finish. For these reasons, inter alia, it is highly desirable that some handy, compact and easily operable surface nish comparator be available to the industry, i. e., manufacturers, inspectors, engineers, designers, etc.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Fig. 1 is a longitudinal sectional View of a finish comparator which embodies my invention.

Fig. 2 is an end view taken substantially in the direction of line 2-2 of Fig. 1.

Fig. 3 is an end view taken substantially in the direction of line 3-3 of Fig. 1.

Fig. 4 is a section taken substantially on line 4 4 of Fig. 1.

Fig. 5 discloses a longitudinal section through a modified comparator. v

Fig. 6 discloses a section taken substantially on line 6--6 of Fig. 5.

In the particular embodiment of this invention disclosed in the drawing ten separate standard finish specimens Illa., Ib, Ic, Illd, Ie, IIJf, Ig, Ih, Iz, Illy' are shown concentrically mounted on the axially extending spindle II, but it is understood that spindle II may be made longer or shorter so as to accommodate more or fewer of the standard finish specimens.

Spindle II has a reduced threaded portion I Ia for a jam nut I3. The finish specimens IUa-Ij are held on the spindle between the jam nut I3 and split resilient ring I4 which abuts against spindle shoulder I Ib and tends to keep the finish specimens Illa-Illy in contact with one another by exerting a lock washer action on jam nut I3. Shoulder IIb may be considered to be a stop. Thus provision is madeto prevent the jam nut from becoming loose and also toikeep the finish specimens in contact with one another when the instrument is subjected to large temperature variations. One end llc of the spindle II has rolled knurling thereon so as to facilitate manual handling of the instrument.

The finish specimens Iw-I05i are made round and each one of them has a flat surface I2 thereon so that the finish on rounded articles as well as the finish on fiat articles may be compared with the corresponding parts on the comparator.

With finish specimens having a 'My' outside diameter, a suitable handy instrument has been made in which each finish specimen was approximately one-half of an inch in length, but the exact length of the finish specimens may be conveniently made shorter or longer than one-half of an inch; also, the exact diameter of the specimens and spindle may be made less or greater than 'V8 inch.

The particular diameter of the finish specimen is not critical and as a matter of fact articles having curved surfaces differing greatly from the curvature on the finishspecimens may be compared with specimens having a diameter of VAS,

i. e., the character of light refiection from rounded objects having differing curvatures is not critical to an observer and therefore a finish speciment for every possible` article curvature is not essential.

The specimens Illa, I 0b are of nickel steel, have a Society of Automotive Engineers (S. A, E.) number of 2330 and represent two degrees of an ff surface finish.

The specimens. I0c, I0d are of carbon steel, have an S. A. E. number of 1035 and represent two degrees of an f surface finish.

The specimens I0e, I0f are of molybdenum steel, have an S. A. E. number of X4l30 and represent two degrees of an fg surface finish.

The specimens I0g, |071, are of carbon steel,

i have an S. A. E. number of 1112 and represent two degrees of a cf surface finish.

The specimens I 0i, |07' are of carbon steel, have an S. A. E. number of 1112 and represent two degrees of a g surface finish,

The specimens have finishes denoted by g, cf, f, ff and fg and these finishes are characterized by the following standards.

AAt present no specific system of symbols has been established, since various Government departments and various manufacturing establishments employ different symbols for the various finishes; therefore, a system of symbols which is standard for the particular using industry will be stamped, etched or engraved or otherwise marked on the specimens.

The particular grades of steel used for the various finish specimens are those representative of' the types of steels upon which the particular grades of finishes are applicable. Also, the particular grade of steel employed as a standard is of the types used for a particular manufacture, coupled with the surface finish requirement for that particular manufacture. Also, in cases where the comparison of the appearance is not as essential as the height and distance between irregularities, the specimens can be made of one kind or grade of steel, i. e., stainless or non-corrosive steel.

A piece of stock in order to have an ff finish may be produced by any suitable cutting or form-` ing tool which will produce a surface having an rms reading of .000008 to .000032 inch as obtained by the conventional brush or profilometer methods. It shall be suitable for bearings or shafts revolving at low speeds or held actually stationary or for other surfaces moving upon one another slowly. A second degree of the ff finish may be a smooth lapped and polished finish with an rms reading of .000001 to .000004 inch.

A piece of stock in order to have an f finish requires a machine finish of good quality, such as is properly applicable to surfaces fitting together but not moving on each other. This finish may be produced with either flat or V shaped tools permitting scoring (tool marks) with a maximum surface roughness having an rms reading of .000250 inch. A second and third degree of the f finish may be a smooth machine finish with maximum rms readings of .000125 and .000063 inch, respectively.`

A piece of stock having an fg finish has an ordinary grind finish with an rms reading of .000008 to .000016 inch. A second degree of an fg finish is one having a profilometer rms reading of .000001 to .000004 inch and which includes lapping and polishing.

The of finish denotes a coarse finish and requires a coarse machine, chipped, or grind finish applicable to clearance cuts or surfaces which are finished to insure the avoidance of interference, or excess metal in cast, forged, etc. parts. A second degree of this cf finish is one just suitable for painted surfaces when appearance is important. The rms values for this class of finish may vary from 500 to 4000 micro inches depending upon the nature of the work involved.

The g finish denotes a coarse grind finish, and to produce this finish it is necessary only to remove undue rough edges from castings or forgings, etc.

The particular enumerated specimens described above are representative of 'the range of surface finishes which might be compared and it is apparent that a greater or less numberl of specimens might be placed on the comparator spindle II and that their particular finish might be different from these described. Also, the particular values ascribed to the various types of finishes maybe modified to have other roughness value ranges.

Specimens of the same type of surface finish might be separated by auxiliary spacers on the spindle II or a V notch 25 may be formed at the junction of different types of surface finish so that the observer might readily distinguish between different types of surface finish.

It is obvious that the specimens Illa-|07' may be easily removed by unsorewing the jam nut I3; other similar specimens may be substituted for one or all of the specimens removed. This last .feature is particularly advantageous since then specimens which are cut from the same piece of stock may be placed on the spindle of one or more of the instruments located at different places in a manufacturing plant or different localities. Since one large piece of machinedstock may be cut into a plurality of small specimens having the same finish, successive specimens of the same finish may be easily inserted on the instrument spindle periodically as the finish on the particular specimen on the instrument becomes tarnished or` polished in use, with the net result that the standard of finish on the comparator remains practically constant over a period of time. If the specimens could not be replacedA on the comparator spindle easily, and the specimens were of steel other than stainless steel, it would be necessary to immerse the comparator in oil to prevent tarnishing of the specimen surface and in that case ,the specimens would become polished due tothe action of the inspector or other user when he wipes the oil from the specimens on the comparator.

In the modification shown in Fig. 5, a locking ring similar to ring I4 is dispensed with, the spindle Il is made tubular and with inner screw threads lla' for the reception of one of a plurality of screw threaded extensions I Ib' having various lengths. One end of the extension Hb has a tapped hole for the reception, of retaining` nut I3'. Advantages of this design are:

light weight, and adaptability for the mounting of fewer or a greater number of specimens. Specimens on Fig. 5 which are similar to those in Fig. 1 are characterized by primed reference numerals.

Fig. 6 discloses a section through a modied specimen 10d having two flat surfaces l2', I2 thereon for comparing flat surfaces. The nish specimens disclosed herein are made round for comparison of round surfaces; however, one or more flat surfaces on these round specimens may be provided with similar grades, degrees or types of surface nishes.

If it is desired to represent flat surface finishes produced by different tools, i. e., by surface grinding, periphery wheel grinding, p-laning or with a shaper, several flat surfaces on the periphery of individual round specimens are provided by these types of tools with the several surface finishes produced thereby having the same' or approximately the same surface roughness value.

The round specimens may be provided to represent nishes produced by different tools or methods yet having the same surface roughness values, the surface roughness value being measured with a suitable instrument. The object of this arrangement of specimens is to enable the inspector or observer to compare the kind of iinish produced by differentl means; articles having the same roughness value and produced by different conventional tools or methods do not always have the same appearance or feeL In order to truly represent the exact appearance and quality of the work to be compared the material of the specimen should preferably be of the same kind and grade as the material being compared, and the surface quality thereon should be produced by the same method, i. e., by the same kind of tools which are of the same material and design. However, since this is not practicable in most instances, the next best procedure is to choose the specimen metal so as to be representative of'a certain class or type of metals best suited or most widely used. Comparators similar' to the ones disclosed herein are extremely useful in comparing surface nish or surface roughness even though the material is not of the same grade or quality when the specimens and component parts ofl the comparator are made of stainless or corrosion resistant steel. Such specimens represent to a high degree the surface nish or roughness of parts made of other kinds or types of steel or other metals; this is true when using the visual and/ or feel methods.

I claim:

An article of manufacture, a surface nish comparator comprising a plurality of cylinders having different physical surface finishes and mounted on a spindle, at least one of Which cylinders has a fiat portion agreeing in finish with the inish of the rest of the cylinder, for comparison with the surface nish of 'flat articles.

EPHRAIM J. ALMQUIST. 

